Blood calcium: tightly regulated by parathyroid hormone, vitamin D, and the kidneys.
What it is
Total calcium in mmol/L includes protein-bound and free fractions. Albumin-adjusted calcium is preferred when albumin is abnormal. Significant abnormalities are often confirmed on a repeat fasting sample.
Total calcium includes ionised and protein-bound fractions. UK labs report mmol/L. Significant abnormalities are confirmed and investigated: calcium is tightly regulated for a reason.
Why it matters
High or low calcium can relate to parathyroid disease, vitamin D status, malignancy, kidney disease, or sample factors. Symptoms (stones, bones, groans, psychiatric moans, the old mnemonic) are prompts for medical care, not supplement experiments.
This guide is educational only and cannot diagnose you. Discuss results, especially anything outside your laboratory’s reference interval, or that does not match how you feel, with a GP or other appropriately qualified clinician.
How it affects the body
Ionised calcium is essential for nerve firing, muscle contraction (including heart), and clotting. Hormonal axes keep it in a narrow band; small blood changes can matter clinically.
Ionised calcium triggers neurotransmitter release and muscle contraction, including cardiac muscle. PTH, vitamin D, and calcitonin axes (with the kidneys and bone) defend the narrow blood range.
For athletes
Bone-loading athletes still need medical review of abnormal calcium, do not assume “bone turnover from training”. Check vitamin D and PTH pathways under guidance.
Bone stress and low energy availability call for a proper bone-health panel under clinical care, not ad-hoc calcium megadoses that can harm if unneeded.
